Electromagnetic device

ABSTRACT

An electromotive device includes an outer casing, a shaft supported by the outer casing, a bobbin disposed inside the outer casing so as to be disposed around the shaft on a common axis with the shaft, and a coil embedded in an outer molding, the coil being constructed by winding a conducting wire onto the bobbin, the bobbin and the outer molding being composed of an epoxy resin, which is an electrically-insulating material resistant to permeation by sulfur compounds.

[0001] This application is based on Application No. 2000-327223, filedin Japan on Oct. 26, 2000, the contents of which are hereby incorporatedby reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an electromagnetic device suchas a stepping motor, a solenoid valve, or the like, used in anautomotive continuously variable transmission, for example.

[0004] 2. Description of the Related Art

[0005]FIG. 4 is an external view of a permanent-magnet stepping motor,FIG. 5 is a cross section taken along line V-V in FIG. 4, FIG. 6 is across section taken along line VI-VI in FIG. 5, FIG. 7 is a crosssection taken along line VII-VII in FIG. 5, and FIG. 8 is a partialexploded perspective of the stepping motor in FIG. 5.

[0006] In the figures, a permanent-magnet (PM) stepping motor 1, whichis immersed and used in an oil, includes: an outer casing 2 made of aresin; a tubular housing 12 made of a resin which is linked to the outercasing 2; a motor main body 3 disposed inside the outer casing 2; ashaft 4 functioning as a moveable shaft rotated by the motor main body3; and a conversion mechanism 31 for converting rotation of the shaft 4into rectilinear motion. Moreover, the outer casing 2 and the housing 12constitute a cover.

[0007] The motor main body 3 includes a pair of stators 5 secured to theouter casing 2, and a rotor 6 secured to the shaft 4. The stators 5have: coils 7 which are each constructed by winding a conducting wire inwhich an electrically-insulating layer is formed on a copper wiresurface; coil terminals 8 led out from the coil 7; connector terminals 9connected to the coil terminals 8; and an external connector 25connected to the connector terminals 9. The rotor 6 has a bush 10secured to the shaft 4, and a circumferentially-magnetized hollowcylindrical permanent magnet 11 fitted over and secured to the bush 10.

[0008] The housing 12 is fastened to the outer casing 2 by a pluralityof screws 12A extending parallel to the shaft 4. A circular interfittingaperture 2 a is formed in the outer casing 2, and an interfittingportion 12 a for inserting into the interfitting aperture 2 a is formedon the housing 12. As shown in FIG. 6, three positioning projections 12b, which protrude radially and come into contact with an innercircumferential surface of the interfitting aperture 2 a, are formed onan outer circumferential surface of the interfitting portion 12 a.Furthermore, an annular groove 12 c is formed in a joining surface ofthe housing 12, where the housing 12 joins the outer casing 2.

[0009] A housing communicating aperture 12 d communicating betweeninternal and external portions of the housing 12 is disposed in a sidesurface portion of the housing 12. A filter 13 for catching contaminantscontained in the oil is disposed in the housing communicating aperture12 d. The shaft 4 is rotatably held by a casing bearing 14 and a housingbearing 15. The housing bearing 15, which is secured inside the housing12, is a rubber-seal type.

[0010] A rod 16 reciprocated in an axial direction of the shaft 4 byrotation of the shaft 4 is disposed at a tip portion of the housing 12.A base-end portion of the rod 16 is inserted inside the housing 12, anda tip portion of the rod 16 protrudes from the tip portion of thehousing 12. A rod communicating aperture 16 a communicating between theinternal portion of the housing 12 and an internal portion of the rod 16is formed in the rod 16. A sleeve 17 for guiding rectilinear motion ofthe rod 16, an oil seal 18 for preventing penetration of contaminantsfrom an outer circumferential portion of the rod 16, and a ring-shapedstopper 19 for regulating progression of the rod 16 are each secured toan inner circumferential surface of the tip portion of the housing 12.

[0011] The conversion mechanism 31 includes a thread portion 4 a, aguide member 20 made of a resin which is formed in the base-end portionof the rod 16 and is engaged with the thread portion 4 a, and a stopper21 made of a metal which is secured to the shaft 4 and regulatesregression of the rod 16. Stopper surfaces 20 b and 21 a which areperpendicular to the direction of rotation of the shaft 4 are formed onthe guide member 20 and the stopper 21, respectively. As shown in FIG. 7a rotation-regulating projection portion 20 a which protrudes radiallyand regulates rotation of the rod 16 is formed on an outercircumferential portion of the guide member 20. Consequently, the guidemember 20 is displaced in an axial direction of the shaft 4 by rotationof the shaft 4. An operating member 22 made of a resin is mounted to thetip portion of the rod 16.

[0012] A construction of each of the stators 5 will now be explained indetail with reference to FIGS. 9 to 12.

[0013] As shown in FIG. 10, the coils 7 are each constructed by windinga conducting wire 50, shown in FIG. 9, formed by coating a copper wire51 with an electrically-insulating layer 52 composed of a polyimideresin, which is a thermoplastic resin, onto a bobbin 53 composed ofnylon, which is a thermoplastic resin, for a predetermined number ofwinds. Then, end portions of the conducting wire 50 of each coil 7 areconnected to the coil terminals 8 mounted to the bobbin 53. Furthermore,as shown in FIG. 11, the coil 7 wound onto the bobbin 53 is embedded inan outer molding 54 composed of nylon, which is a thermoplastic resin.In addition, as shown in FIG. 12, cores 55 made of iron are disposed soas to surround the coil 7, completing the construction of the stator 5.

[0014] The stepping motor 1 constructed in this manner is mounted to anautomobile continuously variable transmission, for example, and theoperating member 22 attached to the tip portion of the rod 16 is engagedwith a link 40 which opens and closes a transmission control valve inthe continuously variable transmission.

[0015] When an electric current is passed through the external connector25, the coils 7 are magnetized, rotating the rotor 6 and the shaft 4together. The guide member 20 is engaged in the thread portion 4 a onthe shaft 4, and since rotation of the guide member 20 is regulated,rotation of the shaft 4 is converted into rectilinear motion of theguide member 20 and the rod 16.

[0016] The transmission control valve is opened and closed through thelink 40 by reciprocation of the rod 16, ultimately changing therotational velocity ratio between the drive shaft and the engine shaft.

[0017] The conventional stepping motor 1 is mounted to an automobilecontinuously variable transmission, for example, and is entirelyimmersed in the oil, which contains sulfur and organosulfur compounds.Furthermore, the coils 7 of the stators 5 are covered by the bobbins 53and the outer moldings 54 which are composed of the thermoplastic resin,and the conducting wires 50 of the coils 7 are constructed by coatingthe copper wire 51 with the electrically-insulating layer 52, which iscomposed of the thermoplastic resin. For that reason, the sulfur and theorganosulfur compounds in the oil permeate the bobbins 53 and the outermoldings 54, and in addition permeate the electrically-insulating layer52, reaching the copper wire 51. As a result, chemical reactions occurat the surface of the copper wire 51 and organosulfur compounds areformed on the surface of the copper wire 51, giving rise to a state ofdecreased adhesive strength of the electrically-insulating layer 52 tothe copper wire 51.

[0018] One problem has been that in this state, theelectrically-insulating layer 52 may be breached due to interferencebetween adjacent conducting wires 50 caused by repeated thermalexpansion and thermal contraction due to the heat history of theconducting wires 50 themselves, leading to wire breakage or shortcircuiting between the conducting wires 50 caused by elution of copperdue to electric potential differences between the conducting wires 50.Another problem has been that breaching of the electrically-insulatinglayer 52 of the conducting wires 50 is more likely at positions wherethe conducting wires 50 and the bobbins 53, which have differentcoefficients of thermal expansion, come into contact, leading to furthershort circuiting or wire breakage.

[0019] Yet another problem has been that when the temperature of the oilbecomes greater than vaporization temperatures of volatile components inthe oil due to heat generated by the coils 7, theelectrically-insulating layer 52 of the conducting wires 50 is morelikely to be permeated by sulfur, etc., and there is a greaterlikelihood of short circuiting occurring between the conducting wires50.

SUMMARY OF THE INVENTION

[0020] The present invention aims to solve the above problems and anobject of the present invention is to provide an electromagnetic devicein which wire-breakage tolerance and short-circuiting tolerance ofconducting wires are improved.

[0021] In order to achieve the above object, according to one aspect ofthe present invention, there is provided an electromotive device used inan oil, the electromagnetic device including:

[0022] an outer casing;

[0023] a moveable shaft supported by the outer casing;

[0024] a bobbin disposed inside the outer casing so as to be disposedaround the moveable shaft on a common axis with the moveable shaft; and

[0025] a coil embedded in an outer molding, the coil being constructedby winding a conducting wire onto the bobbin,

[0026] wherein the bobbin and the outer molding are composed of anelectrically-insulating material resistant to permeation by sulfurcompounds.

[0027] According to another aspect of the present invention, there isprovided an electromotive device used in an oil, the electromagneticdevice including:

[0028] an outer casing;

[0029] a moveable shaft supported by the outer casing;

[0030] a bobbin disposed inside the outer casing so as to be disposedaround the moveable shaft on a common axis with the moveable shaft; and

[0031] a coil embedded in an outer molding, the coil being constructedby winding a conducting wire onto the bobbin,

[0032] wherein the conducting wire is constituted by a copper wire, anelectrically-insulating layer coated on the copper wire, and aprotective layer coated on the electrically-insulating layer, theprotective layer being composed of an electrically-insulating materialresistant to permeation by sulfur compounds.

[0033] According to yet another aspect of the present invention, thereis provided an electromotive device used in an oil, the electromagneticdevice including:

[0034] an outer casing;

[0035] a moveable shaft supported by the outer casing;

[0036] a bobbin disposed inside the outer casing so as to be disposedaround the moveable shaft on a common axis with the moveable shaft; and

[0037] a coil embedded in an outer molding, the coil being constructedby winding a conducting wire onto the bobbin,

[0038] wherein the conducting wire is constituted by a copper wire, ahigh-temperature solder layer coated on the copper wire, and aprotective layer coated on the high-temperature solder layer, theprotective layer being composed of an electrically-insulating materialresistant to permeation by sulfur compounds.

[0039] The electrically-insulating material resistant to permeation bysulfur compounds may be a thermosetting resin.

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Other features, objects and advantages of the present inventionwill become apparent from the following description of preferredembodiments with reference to the drawings in which like referencecharacters designate like or corresponding parts throughout severalviews, and in which:

[0041]FIG. 1 is a cross section showing a stepping motor according toEmbodiment 1 of the present invention;

[0042]FIG. 2 is a cross section showing a conducting wire used in coilsof a stepping motor according to Embodiment 2 of the present invention;

[0043]FIG. 3 is a cross section showing a conducting wire used in coilsof a stepping motor according to Embodiment 3 of the present invention;

[0044]FIG. 4 is an external view of a conventional permanent-magnetstepping motor;

[0045]FIG. 5 is a cross section taken along line V-V in FIG. 4;

[0046]FIG. 6 is a cross section taken along line VI-VI in FIG. 5;

[0047]FIG. 7 is a cross section taken along line VII-VII in FIG. 5;

[0048]FIG. 8 is a partial exploded perspective of the stepping motor inFIG. 5;

[0049]FIG. 9 is a cross section showing a conducting wires used in coilsof the stepping motor in FIG. 5;

[0050]FIG. 10 is a perspective showing a wound state of the coils in astator of the stepping motor in FIG. 5;

[0051]FIG. 11 is a perspective showing a molded state of a resin portionin the stator of the stepping motor in FIG. 5; and

[0052]FIG. 12 is a perspective showing the stator of the stepping motorin FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0053] The preferred embodiments of the present invention will now beexplained with reference to the drawings.

[0054] Embodiment 1

[0055]FIG. 1 is a cross section showing a stepping motor according toEmbodiment 1 of the present invention. Moreover, in the figure, portionswhich are the same as or correspond to those in the conventionalstepping motor will be given the same numbering, and explanationsthereof will be omitted.

[0056] In FIG. 1, coils 7 are each constructed by winding a conductingwire 50, formed by coating a copper wire 51 with anelectrically-insulating layer 52, for a predetermined number of windsonto a bobbin 61 composed of an epoxy resin, which is a thermosettingresin functioning as an electrically-insulating material resistant topermeation by sulfur compounds. Then, end portions of the conductingwire 50 of each coil 7 are connected to coil terminals 8 mounted to thebobbin 61. Furthermore, the coils 7 wound onto the bobbins 61 are eachembedded in an outer molding 62 composed of an epoxy resin, which is athermosetting resin. In addition, cores 55 made of iron are disposed soas to surround the coil 7, constructing a stator 60. Then, two stators60 are disposed surrounding a shaft 4 on a common axis with the shaft 4.

[0057] Moreover, the rest of the construction is the same as for theabove conventional stepping motor 1.

[0058] Now, considering molecular structure, in contrast tothermoplastic resins, which are aggregates of straight-chainmacromolecules, thermosetting resins have a reticulate cross-linkedstructure. Thus, the permeation of sulfur and organosulfur compounds,etc., is extremely low in thermosetting resins compared to thermoplasticresins.

[0059] In a stepping motor 100, which is an electromagnetic deviceconstructed in this manner, because the coils 7 are embedded in theepoxy resin, which is a thermosetting resin, the amount of sulfur andthe organosulfur compounds that permeate the bobbins 61 and the outermoldings 62 from the oil and reach the electrically-insulating layer 52is significantly lowered. As a result, formation of sulfur compounds ona surface of the copper wire 51 resulting from chemical reactionsbetween the sulfur and the copper wire 51 and between the organosulfurcompounds and the copper wire 51 is suppressed, and reductions inadhesive strength of the electrically-insulating layer 52 to the copperwire 51 are suppressed.

[0060] Thus, even if there is interference between adjacent conductingwires 50 caused by repeated thermal expansion and thermal contractiondue to the heat history of the conducting wires 50 themselves, damage tothe electrically-insulating layer 52 is suppressed, and wire breakageand short circuiting between the conducting wires 50 caused by elutionof copper due to electric potential differences between the conductingwires 50 are suppressed.

[0061] Furthermore, because damage to the electrically-insulating layer52 of the conducting wire 50 at positions where the conducting wire 50and the bobbins 61, which have different coefficients of thermalexpansion, come into contact, is also suppressed, short-circuitingtolerance and wire-breakage tolerance of the conducting wire 50 isimproved.

[0062] In addition, even if the temperature of the oil becomes greaterthan vaporization temperatures of volatile components in the oil due toheat generated by the coils 7, the likelihood of sulfur, etc.,permeating the bobbins 61 and the outer moldings 62 and reaching theelectrically-insulating layer 52 of the conducting wire 50 is reduced,ensuring the short-circuiting tolerance and the wire-breakage toleranceof the conducting wire 50.

[0063] Embodiment 2

[0064]FIG. 2 is a cross section showing a conducting wire used in coilsof a stepping motor according to Embodiment 2 of the present invention.

[0065] In FIG. 2, a conducting wire 63 is formed by additionally coatinga protective layer 64 composed of epoxy resin, which is a thermosettingresin functioning as a electrically-insulating material resistant topermeation by the sulfur compounds, on the electrically-insulating layer52 which is coated on the copper wire 51.

[0066] Moreover, the construction of Embodiment 2 is the same as inEmbodiment 1 except for the fact that the conducting wire 63 is used inplace of the conducting wire 50.

[0067] In Embodiment 2, because the protective layer 64, which has lowpermeability to the sulfur and organosulfur compounds, is coated on theelectrically-insulating layer 52, the sulfur and organosulfur compoundspermeating the bobbins 61 and the outer moldings 62 from the oil areblocked by the protective layer 64 from reaching theelectrically-insulating layer 52.

[0068] Thus, according to Embodiment 2, because the amount of the sulfurand organosulfur compounds reaching the electrically-insulating layer 52is further reduced compared to Embodiment 1, the short-circuitingtolerance and the wire-breakage tolerance of the conducting wire 50 arestill further improved.

[0069] Now, in Embodiment 2 above, the bobbins 61 and the outer moldings62 used are composed of the epoxy resin, which is anelectrically-insulating material resistant to permeation by the sulfurcompounds, but bobbins and outer moldings composed of any thermoplasticresin may be used. In that case, even if the sulfur and organosulfurcompounds in the oil permeate the bobbins 61 and the outer moldings 62,because the sulfur and organosulfur compounds are blocked by theprotective layer 64 from reaching the electrically-insulating layer 52,the short-circuiting tolerance and the wire-breakage tolerance of theconducting wire are improved compared to the conventional example.

[0070] Embodiment 3

[0071]FIG. 3 is a cross section showing a conducting wire used in coilsof a stepping motor according to Embodiment 3 of the present invention.

[0072] In FIG. 3, a conducting wire 65 is formed by coating ahigh-temperature solder layer 66 onto the copper wire 51, and coatingthe protective layer 64 on the high-temperature solder layer 66. Here, alead-rich tin-lead solder having 90 wt % or more of lead is used for thehigh-temperature solder layer 66.

[0073] Moreover, the construction of Embodiment 3 is the same as inEmbodiment 1 except for the fact that the conducting wire 65 is used inplace of the conducting wire 50.

[0074] In Embodiment 3, because the protective layer 64, which has lowpermeability to the sulfur and organosulfur compounds, is coated on thehigh-temperature solder layer 66, the sulfur and organosulfur compoundspermeating the bobbins 61 and the outer moldings 62 from the oil aresuppressed by the protective layer 64 from reaching the high-temperaturesolder layer 66. Then, any sulfur and organosulfur compounds which dopermeate the protective layer 64 are prevented by the high-temperaturesolder layer 66 from reaching the copper wire 51. Now, thehigh-temperature solder is less likely to react with the sulfur andorganosulfur compounds than copper. Thus, sulfur compounds are notformed on the surface of the high-temperature solder layer 66 as aresult of chemical reactions between the sulfur and organosulfurcompounds and the high-temperature solder layer 66 and there is nodecrease in adhesive strength of the protective layer 64 to thehigh-temperature solder layer 66. As a result, the short-circuitingtolerance and the wire-breakage tolerance of the conducting wire 65 arestill further improved.

[0075] Now, in Embodiment 3 above, the bobbins 61 and the outer moldings62 used are composed of the epoxy resin, which is anelectrically-insulating material resistant to permeation by the sulfurcompounds, but bobbins and outer moldings composed of any thermoplasticresin may be used. In that case, even if the sulfur and organosulfurcompounds in the oil permeate the bobbins 61 and the outer moldings 62,because they are blocked by the protective layer 64 and thehigh-temperature solder layer 66 from reaching the copper wire 51, theshort-circuiting tolerance and the wire-breakage tolerance of theconducting wire are improved compared to the conventional example.

[0076] Moreover, each of the above embodiments has been explained usingan epoxy resin, which is a material having low permeability to sulfurand organosulfur compounds, that is, an electrically-insulating materialresistant to permeation by sulfur compounds, but any thermosetting resinmay be used as an electrically-insulating material resistant topermeation by sulfur compounds, for example, a phenol resin.

[0077] Each of the above embodiments has been explained with referenceto stepping motors, but the present invention is not limited to steppingmotors; it may be applied to any electromagnetic device used in an oil,for example, to a solenoid valve for controlling the action of atransmission mechanism for adjusting the rotational velocity ratiobetween a drive shaft and an engine shaft by regulating an oil channelusing a movable valve to control oil flow rate or pressure.

[0078] In Embodiment 3 above, the high-temperature solder layer 66 isformed using tin-lead solder having 90 wt % or more of lead, but it isnot necessary for the lead content in the tin-lead solder to be 90 wt %or more; the lead content need only be 60 wt % or more.

[0079] Although the preferred embodiments of the present invention havebeen described above, it should be understood that the present inventionis not limited thereto and that other modifications will be apparent tothose skilled in the art without departing from the sprint of theinvention.

[0080] The scope of the present invention, therefore, should bedetermined solely by the appended claims.

[0081] This electromotive device of the present invention is constitutedas described above. Thus, this electromotive device has the followingeffects.

[0082] According to one aspect of the present invention, there isprovided an electromotive device used in an oil, the electromagneticdevice including:

[0083] an outer casing;

[0084] a moveable shaft supported by the outer casing;

[0085] a bobbin disposed inside the outer casing so as to be disposedaround the moveable shaft on a common axis with the moveable shaft; and

[0086] a coil embedded in an outer molding, the coil being constructedby winding a conducting wire onto the bobbin,

[0087] wherein the bobbin and the outer molding are composed of anelectrically-insulating material resistant to permeation by sulfurcompounds, preventing wire breakage or short circuiting betweenconducting wires resulting from sulfur and organosulfur compounds in theoil permeating the bobbin and the outer molding and reaching theconducting wire, thereby providing an electromagnetic device enablingimproved short-circuiting tolerance and wire-breakage tolerance in theconducting wire.

[0088] According to another aspect of the present invention, there isprovided an electromotive device used in an oil, the electromagneticdevice including:

[0089] an outer casing;

[0090] a moveable shaft supported by the outer casing;

[0091] a bobbin disposed inside the outer casing so as to be disposedaround the moveable shaft on a common axis with the moveable shaft; and

[0092] a coil embedded in an outer molding, the coil being constructedby winding a conducting wire onto the bobbin,

[0093] wherein the conducting wire is constituted by a copper wire, anelectrically-insulating layer coated on the copper wire, and aprotective layer coated on the electrically-insulating layer, theprotective layer being composed of an electrically-insulating materialresistant to permeation by sulfur compounds, preventing wire breakage orshort circuiting between conducting wires resulting from sulfur andorganosulfur compounds in the oil permeating the bobbin and the outermolding and reaching the copper wire, thereby providing anelectromagnetic device enabling improved short-circuiting tolerance andwire-breakage tolerance in the conducting wire.

[0094] According to yet another aspect of the present invention, thereis provided an electromotive device used in an oil, the electromagneticdevice including:

[0095] an outer casing;

[0096] a moveable shaft supported by the outer casing;

[0097] a bobbin disposed inside the outer casing so as to be disposedaround the moveable shaft on a common axis with the moveable shaft; and

[0098] a coil embedded in an outer molding, the coil being constructedby winding a conducting wire onto the bobbin,

[0099] wherein the conducting wire being constituted by a copper wire, ahigh-temperature solder layer coated on the copper wire, and aprotective layer coated on the high-temperature solder layer, theprotective layer being composed of an electrically-insulating materialresistant to permeation by sulfur compounds, preventing wire breakage orshort circuiting between conducting wires resulting from sulfur andorganosulfur compounds in the oil permeating the bobbin and the outermolding and reaching the copper wire, thereby providing anelectromagnetic device enabling improved short-circuiting tolerance andwire-breakage tolerance in the conducting wire.

[0100] The electrically-insulating material resistant to permeation bysulfur compounds may be a thermosetting resin, facilitating formation ofthe bobbin, the outer molding, and the protective layer.

What is claimed is:
 1. An electromotive device used in an oil, saidelectromagnetic device comprising: an outer casing; a moveable shaftsupported by said outer casing; a bobbin disposed inside said outercasing so as to be disposed around said moveable shaft on a common axiswith said moveable shaft; and a coil embedded in an outer molding, saidcoil being constructed by winding a conducting wire onto said bobbin,wherein said bobbin and said outer molding are composed of anelectrically-insulating material resistant to permeation by sulfurcompounds.
 2. The electromotive device according to claim 1 wherein saidelectrically-insulating material resistant to permeation by sulfurcompounds is a thermosetting resin.
 3. An electromotive device used inan oil, said electromagnetic device comprising: an outer casing; amoveable shaft supported by said outer casing; a bobbin disposed insidesaid outer casing so as to be disposed around said moveable shaft on acommon axis with said moveable shaft; and a coil embedded in an outermolding, said coil being constructed by winding a conducting wire ontosaid bobbin, wherein said conducting wire is constituted by a copperwire, an electrically-insulating layer coated on said copper wire, and aprotective layer coated on said electrically-insulating layer, saidprotective layer being composed of an electrically-insulating materialresistant to permeation by sulfur compounds.
 4. The electromotive deviceaccording to claim 3 wherein said electrically-insulating materialresistant to permeation by sulfur compounds is a thermosetting resin. 5.An electromotive device used in an oil, said electromagnetic devicecomprising: an outer casing; a moveable shaft supported by said outercasing; a bobbin disposed inside said outer casing so as to be disposedaround said moveable shaft on a common axis with said moveable shaft;and a coil embedded in an outer molding, said coil being constructed bywinding a conducting wire onto said bobbin, wherein said conducting wireis constituted by a copper wire, a high-temperature solder layer coatedon said copper wire, and a protective layer coated on saidhigh-temperature solder layer, said protective layer being composed ofan electrically-insulating material resistant to permeation by sulfurcompounds.
 6. The electromotive device according to claim 5 wherein saidelectrically-insulating material resistant to permeation by sulfurcompounds is a thermosetting resin.